Flashguns

ABSTRACT

A flashgun using flashbulbs is provided for taking photographs by artificial light. The ignition of the flashbulb is initiated by the flash contact of the camera and an ignition circuit is connected to a primary coil of a transformer. The secondary coil of the transformer is connected to the firing circuit of a thyristor which on conduction energizes an electromagnet of a locking device for holding a shutter in front of the flashbulb in the open position. An electronic switching device including a photosensitive resistor controls a holding magnet cooperating with the drive of the shutter for releasing the shutter at the end of a time interval formed by the electronic switching device in order to allow the shutter to close.

United States Patent Rentschler et al. Feb. 29, 1972 [541 FLASHGUNS3,245,332 4/1966 Kagan ..95/53 [72] inventors: Waldemar T. Rentschler;Winiried Espig, 335 122? 95/53 EB o Pi l la9k i E j pl imgy [73]Assignee: Prontor-Werk Alfred Gauthier G.m.b.l-l., Primary ExaminerJohnM. Horan Calmbach, Black Forest, Germany Assistant Examiner-Robert P.Greiner [22] Filed, i Attorney-March, Le Fever& Wyatt [2]] Appl. No.2806,161 [57] ABSTRACT A flashgun using flashbulbs is provided for takingphotographs [30] Foreign Application Priority Data by artificial light.The ignition of the flashbulb is initiated by the flash contact of thecamera and an ignition circuit is con- Mar. 14,1968 Germany ..P 1622941.7 meted toaprimary conofauansformenThe secondary co of thetransformer is connected to the firing circuit of a Cl "95/115 95/ mthyristor which on conduction energizes an electromagnet of a l 58]Field M Search 31 10 0 locking device for holding a shutter in front ofthe flashbulb in the open position. An electronic switching deviceincluding a photosensitive resistor controls a holding magnetcooperating with the drive of the shutter for releasing the shutter atthe end [56] References cued of a time interval formed by the electronicswitching device in UNlTED STATES PATENTS order to allow the shutter toclose.

3,491,667 H1970 Land ..95/ l l 7 Claims, 2 Drawing Figures I x I p W201/ 41 T3 i 1 ll 42 I O O 7 a O O FLASHGUNS The invention relates to aflashgun using flashbulbs for making artificial light exposures.

The invention is more particularly concerned with a flashgun in whichthe flashbulb has a shutter between it and the object to bephotographed, actuated means of a driving device, the shutter being openat the beginning of the combustion of the bulb to allow direct lightirradiation of the object. The

7 driving device is so controlled by means of an electronic switchingdevice including a photosensitive resistor in its circuit, that theshutter closes after a time interval dependent on the intensity of thelight reflected from the object. The advantage of this gun, comparedwith conventional flashguns, is that it is able automatically to shutoff the light from the flashbulb before the ending of its actuallighting period, which in turn enables cumbersome and time-wastingsetting operations to be dispensed with when taking photographs by flashlight.

The present invention enables a flash gun of the kind referred, to beused in any camera fitted with X-contact, while at the same timeensuring that the correct light irradiation of the object occurs withina preselected exposure time interval of one-thirtieth sec., usual forflash exposures.

In accordance with the invention, the ignition of the flashbulb isinitiated by the synchro-contact of the camera. In the ignition circuitof the bulb there is a-primary coil of a transformer whose secondarycoil is connected to the firing circuit of a thyristor. Firing of thethyristor energizes an electromagnet of a locking device which retainsthe shutter open against spring tension. An electronic device, includinga photosensitive resistor, controls a holding magnet which cooperateswith the drive of the shutter to release the latter at the end of a timeinterval formed by the switching device at the end of which the shuttercloses. In this way, when taking flash photographs with a presetexposure time usual for this kind of photograph, it is ensured that,when the flashbulb is ignited by means of the X-contact normallyprovided in cameras, the light irradiation of the objects occurs withinthe preset exposure time. The

I simultaneous setting off of flashbulb and thyristor ensures that atthe commencement of ignition of the flashbulb the electronic switchingdevice is connected to potential and the mechanical locking deviceretaining the shutter in front of the flashbulb in the open position, isput out of action early enough to allow the electronic switching deviceto close the shutter after the correct time interval.

According to a feature of the invention, the locking device serving tokeep the shutter open, cooperates directly with the shutter drive, orwith a cocking member for moving it into the cocked position.

A further feature of the invention consists in that the armature of theholding magnet is arranged on an intermediate lever which in turn ismounted on a lever serving to drive the shutter, and is resilientlysupported thereon. This provides a reliable abutment of the armature ofthe holding magnet, with simultaneous locking of the shutter. In orderfrom a functional point of view to provide the most favorable conditionsfor the mechanical locking device, provision is made for theelectromagnet to be formed as a tractor magnet.

Details of the invention are shown below with reference to a flashgunthe shutter of which comprises two flaps. The invention is applicablealso to flashguns which are provided with roller blind shutters, and/orwhich use flash cubes as the light source. I

In the accompanying drawings,

FIG. 1 shows a horizontal section of the flashgun in the cockedposition;

FIG. 2 is a circuit diagram of the electronic control for the flashgun.

In the Figures, 1'' denotes the housing of the flashgun, the electroniccircuit of which is electrically connected by means of a cable 2' and aplug 3" with the synchronous contact S of a camera. A lever 13" which atone end is rotatably mounted and at the other end is adapted to belocked by an electromagnetic locking device against the action of aspring in the cocked position, is used to drive the shutter 7", 8",which consists of two rotatable flaps. The driving lever 13" which isoperationally connected via a pin and slot connection with the shutter7", 8", is adapted to be moved into the cocked position by means of apress-button 22" biased by a spring 23". The electromagnetic lockingdevice has an electromagnet 19", an armature lever 20", a catch spring16" and cooperating therewith a supporting spring 17" moved by thearmature lever 20". The mechanical locking device formed by the twosprings 16" and 17" may be replaced by an alternative locking deviceacting on the press-button 22". It is essential that either device, whenthe armature lever 20" is attracted by the electromagnet 19" acting as atractor magnet, should be instantly moved out of the locking position.For this purpose a locking device could also be provided which isassociated directly with the shutter 7", 8", locking the lattermechanically after it has been moved into the open'or cocked position.This open position is retained until the electronic circuit device,described in detail below, enables the shutter to return to the closedposition, this being initiated by closure of the synchronous contact SAs shown in FIG. 1, the driving lever 13 has associated therewith anelectromagnet 40, which is connected in the circuit device mentionedabove. An armature 41 which is pivotably mounted by means of anintermediate lever 42 hingedly arranged on the driving lever 13'',cooperates with this electromagnet 40, formed as a holding magnet. Thisarrangement ensures that, when moving the driving lever 13" which ispositively connected with the shutter 7", 8" into the cocked position,the armature 41 is reliably abuted against the holding magnet before thelocking of the shutter driving lever by the locking springs 16" and 17As shown by the circuit diagram in FIG. 2, the circuit of an energysource or batter E has a transformer 45 connected therein, together witha synchronous or flash contact S and the flashbulb 6" of the flash gun.The primary coil 45a of the transformer is located in the ignitioncircuit of the bulb 6", whilst the secondary coil 45b thereof is locatedin the firing circuit of a thyristor Ty. The numeral 46 denotes a knownelectronic timing circuit used to control the closing time of theshutter 7", 8" and which is energized when the thyristor Ty fires.Simultaneously with the firing of the thyristor the tractor magnet 19"is energized, disengaging the catch device formed by the two springs 16"and 17" blocking the shutter 7", 8" immediately the synchronous or flashcontact S, closes. 48 is a flash capacitor, 49 is a control capacitorwhich is connected between the secondary coil 45b and the thyristor Ty.By means of switch S which is connected with the RC networks of theelectronic time control circuit 46, the capacitor C the photosensitiveresistor R," the capacitor C and the fixed resistor R a maximumpredetermined timing of say one-thirtieth sec. for closing the shutter7", 8", is determined. The switches S- and 8;, are coupled together asshown by the dotted line, and act to discharge the capacitor C and C,"during the'transfer of the shutter 7", 8" to the closed position. forwhich purpose the two switches are arranged in the movement path of thedriving lever 13' The flashgun described above operates as follows:

To carry out a flash exposure it is first necessary to connect the plug3" of the flashgun to the socket of the synchronous or flash contactprovided on the camera, and to open the shutter itself by depressing thebutton 22" into the cocked position shown in FIG. 1. When, on releasingthe camera, its flash contact S. is actuated, flashbulb 6" is ignited.With the ignition of the flashbulb 6" a surge of current occurs in thesecondary coil 45b of the transformer 45, which surge causes thethyristor Ty to fire. This energizes the tractor magnet 19", and theelectronic time control circuit 46 is energized by switch S The magnet19" instantly attracts the armature lever 20" and thereby releases thecatch springs I6", 17' blocking the shutter open. With the energizing ofthe attracting magnet 19" a magnetic field also simultaneously builds upin the holding magnet 40, and the time control circuit 46 commences tocapacitor C Hence the driving lever 13" is held until the circuit 46trips in dependence on the light incident on the photosensitive resistorR When this occurs, the magnetic field in the holding magnet 40collapses, releasing the driving lever 13', which allows the shutter 7",8" to close under the action of the tension spring During the returnmovement of the driving lever 13'', the two switches S and S are changedover. The changeover of switch S interrupts the anode circuit of thethyristor Ty thus extinguishing it, and the back contact of the switch Sapplies a short circuit to the capacitors C and C resulting in theirdischarge.

The capacitor C and the resistor R are provided to bring about theclosure of the shutter 7 8" after a predetermined time interval of, forexample, one-thirtieth sec. even if the light reflected by the object isso low that the electronic circuit 46 would not operate at all, or wouldoperate only after a long time, measured from the ignition of theflashbulb 6".

This ensures that if the camera ishand held, the resulting photograph,even if underexposed, is not blurred by movement.

What we claim is:

1. A flashgun using flashbulbs for taking photographs by artificiallight including ignition means for the flashbulb initiated by the flashcontact of a camera, the ignition circuit for the flashbulb beingconnected to a primary coil of a transformer, a secondary coil of saidtransformer being connected in the firing circuit of a thyristor whichon conduction, energizes an electromagnet of locking means for holding ashutter in front of a flashbulb in the open position, and electronicswitching means including a photosensitive resistor which controls aholding magnet cooperating with drive means of the shutter to releasesaid shutter at the end of a time interval formed by said electronicswitching means to allow said shutter to close.

2. The flashgun according to claim 1, wherein said locking means servingto hold said shutter open is engageable with a drive member of saidshutter.

3. The flashgun of claim 1 wherein said locking means serving to holdsaid shutter in the open position is engageable with a cocking memberconnected to said shutter for moving said shutter into the cockedposition.

4. The flashgun of claim 3 wherein an armature cooperating with saidholding magnet is arranged on an intermediate lever resiliently mountedon said cocking member, said cocking member being a pivotally mountedlever connected to said shutter for moving said shutter into the openedand closed position.

5. The flashgun of claim 4 wherein said electromagnet cooperating withsaid locking device is a tractor magnet.

6. A flashgun using flashbulbs for taking photographs by artiflciallight including circuit means for igniting the flashbulb by the flashcontact of a cooperating camera, said circuit means having an ignitioncircuit for the flashbulb connected to the primary coil of atransformer, and a secondary coil of said transformer connected in thefiring circuit of a thyristor, locking means having an electromagnetenergized when said thyristor conducts, said locking means having springmembers engageable with a drive member of shutter means for theflashbulb to hold said shutter means in the open position when saidelectromagnet is energized, electronic timing circuit means including aphotosensitive resistor, said electronic timing circuit meanscontrolling a holding magnet cooperating with said drive member of saidshutter means to release said shutter means at the end of the timeinterval formed by said electronic timing circuit means.

7. The flashgun of claim 6 wherein an armature cooperating with saidholding magnet is mounted on an intermediate lever, said intermediatelever being resiliently mounted on said drive member, and wherein saiddrive member is a spring-biased pivotally mounted lever connected tosaid shutter means for moving said shutter into the open and closedposition.

1. A flashgun using flashbulbs for taking photographs by artificiallight including ignition means for the flashbulb initiated by the flashcontact of a camera, the ignition circuit for the flashbulb beingconnected to a primary coil of a transformer, a secondAry coil of saidtransformer being connected in the firing circuit of a thyristor whichon conduction, energizes an electromagnet of locking means for holding ashutter in front of a flashbulb in the open position, and electronicswitching means including a photosensitive resistor which controls aholding magnet cooperating with drive means of the shutter to releasesaid shutter at the end of a time interval formed by said electronicswitching means to allow said shutter to close.
 2. The flashgunaccording to claim 1, wherein said locking means serving to hold saidshutter open is engageable with a drive member of said shutter.
 3. Theflashgun of claim 1 wherein said locking means serving to hold saidshutter in the open position is engageable with a cocking memberconnected to said shutter for moving said shutter into the cockedposition.
 4. The flashgun of claim 3 wherein an armature cooperatingwith said holding magnet is arranged on an intermediate leverresiliently mounted on said cocking member, said cocking member being apivotally mounted lever connected to said shutter for moving saidshutter into the opened and closed position.
 5. The flashgun of claim 4wherein said electromagnet cooperating with said locking device is atractor magnet.
 6. A flashgun using flashbulbs for taking photographs byartificial light including circuit means for igniting the flashbulb bythe flash contact of a cooperating camera, said circuit means having anignition circuit for the flashbulb connected to the primary coil of atransformer, and a secondary coil of said transformer connected in thefiring circuit of a thyristor, locking means having an electromagnetenergized when said thyristor conducts, said locking means having springmembers engageable with a drive member of shutter means for theflashbulb to hold said shutter means in the open position when saidelectromagnet is energized, electronic timing circuit means including aphotosensitive resistor, said electronic timing circuit meanscontrolling a holding magnet cooperating with said drive member of saidshutter means to release said shutter means at the end of the timeinterval formed by said electronic timing circuit means.
 7. The flashgunof claim 6 wherein an armature cooperating with said holding magnet ismounted on an intermediate lever, said intermediate lever beingresiliently mounted on said drive member, and wherein said drive memberis a spring-biased pivotally mounted lever connected to said shuttermeans for moving said shutter into the open and closed position.